The invention relates to the field of compensating buffers for integrated circuits.
As the complexity of personal computers and other systems employing integrated circuits increases, the need for precise output drivers has become more critical. Often an integrated circuit is required to drive signals with frequencies of 100 MHz or higher over printed circuit board traces several inches in length. Such traces behave as transmission lines making the data transfer difficult unless the impedance of the buffers compensates for the transmission line characteristics. Other factors enter into the need for compensated buffers, for instance, temperature and voltage vary during circuit operation which changes the characteristics of the buffers.
Numerous compensating output buffers are known such as shown in U.S. Pat. Nos. 5,578,971; 5,528,166; 4,975,598 and 4,768,170.
In co-pending application U.S. Ser. No. 09/299,771; filed Apr. 26, 1999, entitled xe2x80x9cMethod and Apparatus for Dual Mode Output Buffer Impedance Compensation,xe2x80x9d now U.S. Pat. No. 6,166,563 (assigned to the assignee of the present application) a buffer disclosed with binary-weighted compensating driver legs which are selected during reset or initialization. External pull-up and pull-down resistors are used to allow a determination of which driver legs are needed. The present invention builds upon the buffer described in the above application as will be seen.